Tools used in Lathe Machine

#4 Thread Cutting Tool

4.1 External Thread Cutting Tool

Metric, B.S.W, or American “V” threads are formed by a single-point thread-cutting tool. Its cutting edges are sharpened to the shape and size of the thread to be cut.

The shape of the tool is determined by the included angle at the nose of the tool which should correspond to the angle of the thread. It may be 60° for metric threads or 55° for B.S.W threads.

he included the angle at the nose of the tool which should correspond to the angle of the thread. It may be 60° for metric threads or 55° for B.S.W threads.

The size or cross-section of the cutting edges of the tool depends upon the pitch of the thread. The below figure illustrates an H.S.S. thread-cutting tool.

So for machining different screw threads having different pitches separate tools are used to produce accurate threads. The nose of the tool is pointed, flat, or rounded according to the shape of the root of the thread.

A thread tool gauge is used to check the shape and size of the tool after it has been ground.

4.1.1 Tool for cutting square threads

The side clearance of the tool for cutting square thread is of prime importance in order to prevent the tool from interfering with or rubbing against the vertical flank of the thread.

As a rule, the forward side clearance angle is determined by adding 5° to the helix angle of the thread, and trailing side clearance is obtained by subtracting 5° from the helix angle, if ø is the forward side clearance angle and θ is the trailing side clearance angle, then from the formula:

The width of the cutting edge should be equal to half the pitch of the thread.

Small clearance angle of 1° to 2° are provided at the side of the tool to prevent the surface from ribbing with the work.

4.2 Internal Thread Cutting Tool

The cutting edge of the tool is exactly similar to an external thread cutting tool but the front clearance angle is sufficiently increased as in a boring tool.

The tool is a forged type orbit type and is held on a boring bar. The point of the tool must be set square with the work.

#7 Forming Tool

Turning curved profiles may be affected by using

1. Ordinary lathe tools,

2. Flat forming tools,

3. Circular forming tools.

An ordinary lathe turning tool may serve the purpose where a copying attachment is used to reproduce the form of a template. Flat-forming tools are made of two types:

1. Simple forming tools

2. Flat dovetail forming tools.

1. Simple forming tools

These tools have their cutting edges ground to the shape of the groove, undercut, or thread to be cut.

Flat dovetail-forming tools have a wider cutting edge corresponding to the shape desired. The tail end of the tool is fitted in a special tool holder. No front rake is provided but sufficient front clearance angle is given and it ranges from 10° to 15°.

Regrinding is always done on the top face of the tool which does not alter the form of the tool.

#5 Facing Tool

A facing tool removes metal by its side cutting edges. So no top rake is necessary in a facing tool. The figure shows H.S.S. facing tool intended for finishing operation. The tool has a 2° side cutting edge angle and a 34° end cutting edge angle that can be accommodated in the space between the end of the work and 60° dead center leaving a clearance of 2° on both sides. The standard shank section is 20Χ20, 25Χ25, 32Χ32, 40Χ40, and 50Χ55 all expressed in mm. The length of the tool is 125, 140,170, 200, and 240 mm and the nose radius varies from 0.5 to 1.6 mm.

#7 Forming Tool

Turning curved profiles may be affected by using

1. Ordinary lathe tools,

2. Flat forming tools,

3. Circular forming tools.

An ordinary lathe turning tool may serve the purpose where a copying attachment is used to reproduce the form of a template. Flat-forming tools are made of two types:

1. Simple forming tools

2. Flat dovetail forming tools.

1. Simple forming tools

These tools have their cutting edges ground to the shape of the groove, undercut, or thread to be cut.

Flat dovetail-forming tools have a wider cutting edge corresponding to the shape desired. The tail end of the tool is fitted in a special tool holder. No front rake is provided but sufficient front clearance angle is given and it ranges from 10° to 15°.

Regrinding is always done on the top face of the tool which does not alter the form of the tool.

2. Circular Form Tools

These tools are preferred in production work as a very long cutting surface can be used resulting in longer tool life.

The centre of the tool is set slightly above the centre line of the work to provide an effective front clearance angle on the tool. The tool will rub against the work if the centres are of the same height.

The tool centre is usually higher than the centre line of the lathe by 1/20 to 1/10 of the tool diameter. This height is termed ‘offset’. Regrinding is done by grinding the flat only.

#8 Boring Tool

A boring tool is similar to a left-hand external turning tool so far its cutting edge is concerned.

The tool may be a bit type inserted in a boring bar or holder, or forged type having a tool shank. The figure shows an H.S.S. tool bit inserted in a boring bar.

A boring bar is made of mild steel with slots or holes cut into it to accommodate the tool bit which is locked by an Allen screw. The amount of projection of the cutting edge of the tool from the center of the bar determines the finished hole diameter of the work. The bit is generally inserted at right angles to the center line of the bar for boring a continuous hole passing from one end to the other end. 

#10 Undercutting Tool

Undercutting or grooving tool has a point and form of the cutting edge exactly similar to the form of the required groove.

Clearance angle is given at all the sides of the tool. For the recessing groove cutting edge, the longitudinal feed is employed. The front clearance angle depends upon the bore of the work.

#11 Parting-off Tool

A parting off tool is normally forged and used as bits for cemented carbide tipped tools. Parting off tool is made as narrow as possible to remove the minimum of metal.

The width of the cutting edge range from 3 to 12 mm only. The length of the cutting tool which inserts into the work should be slightly longer than the radius of the bar stock being machined.

As the tool penetrates deep into the work, clearance is provided all around the tool cutting edge to prevent it from rubbing against the work surface.

As the tool is purely ended cutting it has no side rake slight back rake is provided on the tool to promote an easy flow of the ships. 

Lathe Cutting Tools Based on Applying Feed

1. Right-hand tool

2. Left-hand tool

3. Round Nose

#2 Left-Hand Tool

The left-hand tool is shown in the figure. Is that which is fed from the Left to the right-hand end of the lathe bed, i.e. from the headstock to the tailstock end.

The left-hand tool is used for left-hand thread cutting operation or turning operation which leaves a shoulder on the right-hand end of the workpiece.

A left-hand tool has its cutting edge formed on its right-hand end when viewed from the top with its nose pointing away from the operator. A left-hand tool may also be used for facing operation.

#3 Round Nose Tool

A round nose turning tool sown in the figure. Maybe fed from left to the right or from right to the left-hand end of the lathe bed away. For this reason, they have no back rake and side rake.

In some cases, a small back rake is provided on the tool. A round nose turning tool is usually used for finish turning operation.